Testing Fractional doses of COVID-19 Vaccines

Millions of people are being vaccinated against SARS-CoV-2 every day, but the virus is also mutating and spreading fast. Vaccine production is increasing, but supply still constrains vaccinations worldwide. Using lower doses of vaccines could dramatically accelerate vaccination. Available evidence on efficacy is not dispositive but suggests half- or even quarter-doses of some vaccines could be almost as effective as currently-used doses. Even if fractional doses are less effective than standard doses, an epidemiological model suggests they could significantly reduce total infections and deaths. The social value of testing dwarfs the costs. However, firms do not internalize the full social value, a market failure that could be addressed with public funding. Governments could support either experimental or observational evaluations of fractional dosing.